Liquid phase deposited titania coating to enable in vitro apatite formation on Ti6Al4V alloy

A recently developed “GRAPE^® technology” provides titanium or titanium alloy implants with spontaneous apatite-forming ability in vitro, which requires properly designed gaps and optimum heat treatment in air. In this study, titanium alloy and commercially pure (cp) titanium substrates were thermally oxidized in air before aligning pairs of specimens in the GRAPE^® set-up, i.e., titanium alloy and cp titanium substrates were aligned parallel to each other with optimum gap width (spatial design). A liquid phase deposition (LPD) technique was employed for titania coatings on titanium alloy substrate. Then, they were soaked in Kokubo’s simulated body fluid (SBF, pH 7.4, 36.5 °C) for 7 days to confirm the in vitro apatite formation on the substrates under the specific spatial design. Anatase-type titania coatings fabricated by using LPD technique led to the deposition of apatite particles within 7 days and showed apatite X-ray diffraction. On the other hand, thermally oxidized titanium alloy substrate in air and non-treated specimens did not show any apatite X-ray diffraction. These results indicated that the heterogeneous nucleation of apatite induced on anatase-type titania coating prepared by LPD technique when it was aligned parallel to thermally oxidized cp titanium substrate with optimum gap width.     

Biomimetic coatings on titanium: a crystal growth study of octacalcium phosphate

The biomimetic approach allows the coating of metal implants with different calcium-phosphate (Ca-P) phases. Films elaborated at physiological conditions exhibited structures closely resembling those of bone mineral. For instance, octacalcium phosphate (OCP, Ca₈(HPO₄)₂(PO₄)₄ · 5H₂O) crystals have been deposited on titanium through a two-step procedure. After cleaning and etching, Ti6Al4V plates were immersed for 24 h into a simulated body fluid (SBF1). A thin amorphous carbonated Ca-P layer precipitated on the metal substrate. Secondly, these thinly Ca-P coated titanium substrates were immersed for 48 h into another simulated body fluid (SBF2). The thin amorphous carbonated Ca-P layer induced the fast precipitation of a second Ca-P layer of 55 m in thickness composed of OCP crystals. The measurements of Ca and P concentrations versus soaking time in SBF2 showed that the carbonated Ca-P layer partially dissolved before the deposition of the OCP coating. X-ray diffraction (XRD) revealed that OCP crystals grew epitaxially on the substrate. OCP is known to be one of the precursors during the bone mineralization process, thereby, this new generation of biomimetic coatings are promising for orthopedic surgery. © 2001 Kluwer Academic Publishers     

A new high temperature resistant glass-ceramic coating for gas turbine engine components

A new high temperature and abrasion resistant glass-ceramic coating system (based on MgO-Al₂O₃-TiO₂ and ZnO-Al₂O₃-SiO₂ based glass systems) for gas turbine engine components has been developed. Thermal shock resistance, adherence at 90°-bend test and static oxidation resistance at the required working temperature (1000°C) for continuous service and abrasion resistance are evaluated using suitable standard methods. The coating materials and the resultant coatings are characterized using differential thermal analysis, differential thermogravimetric analysis, X-ray diffraction analysis, optical microscopy and scanning electron microscopy. The properties evaluated clearly showed the suitability of these coatings for protection of different hot zone components in different types of engines. XRD analysis of the coating materials and the resultant coatings showed presence of a number of microcrystalline phases. SEM micrographs indicate strong chemical bonding at the metal-ceramic interface. Optical micrographs showed smooth glossy impervious defect free surface finish.     

Incorporation of proteins and enzymes at different stages of the preparation of calcium phosphate coatings on a degradable substrate by a biomimetic methodology

In this work, the possibility of incorporating proteins into calcium phosphate (Ca-P) coatings, prepared on the surface of starch polymeric biomaterials by means of a biomimetic route, was investigated. The morphology, chemical composition and crystallinity of Ca-P coatings was assessed and related to the incorporation of the studied biomolecules. For that, bovine serum albumin (BSA) and α-amylase were added in concentrations of 1 mg/ml to simulated body fluid (SBF) solutions, being both added at the nucleation or growth stages of the biomimetic coating process. A biodegradable blend of corn starch/ethylene vinyl alcohol (SEVA-C) was used as substrate and bioactive glass (45S5 Bioglass®) was used as the nucleating agent. The obtained Ca-P coatings were characterised by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy using an attenuated reflectance device (FTIR-ATR) and thin-film X-ray diffraction (TF-XRD). Additionally, to evaluate the activity of the incorporated enzyme and the stability of the Ca-P films, coated samples were immersed in an SBF solution for different periods of time. The enzyme activity was measured and the morphology of the coating examined by SEM. The results obtained showed that the presence of protein molecules, at the nucleation or growth stages, lead to the formation of a dense Ca-P film presenting different morphologies that were different of the selected coating conditions. FTIR-ATR analysis detected the presence of carbonate and phosphate groups on the Ca-P layer, indicating the formation of a coating similar to the mineral component of vertebrates bone tissue. When proteins were added, amide I and amide II bands, characteristic groups of protein molecules, were also detected, revealing the efficient incorporation of these biomolecules into the Ca-P coatings.Ca-P coatings, with α-amylase incorporated at the nucleation stage, showed no degradation of the film after incubation in SBF for 28 days. The release of increasing concentration of reducing sugars with degradation time revealed that α-amylase was efficiently incorporated in the coating remaining active throughout the coating preparation. This can be a strategy that will allow, in addition of conferring osteoconductive properties to biodegradable polymers, also simultaneously tailoring their degradation kinetics.     

Calcium phosphate coating of Ti–Nb–Zr–Sn titanium alloy

This study focuses on rapid formation of calcium phosphate coating on a β type Ti–Nb–Zr–Sn biomedical titanium alloy by alkali treatment. The results show that a bioconductive surface layer forms on specimens immersed in 1–5 M KOH solution but only treatment in 1 M KOH avoids formation of crevices, producing a potassium titanate layer with porous network structure. Heat treatment at 600 °C after the alkali treatment promotes titanate growth. Following the above treatments, a continuous apatite layer forms within 4 h of soaking in a calcium phosphate solution with high ionic concentration. Such rapid apatite formation is due to high concentration of calcium ions in the solution used in this study and the buffering function of NaHCO₃. Results of dissolution experiment show that Ca and P ions release gradually from the coating during soaking in a 0.9% NaCl solution, which may be helpful to the formation of natural bone if implanted in human body. Cell culture experiment shows that the apatite layer favours adhesion and proliferation of rat osteoblast as compared with coating-free Ti–Nb–Zr–Sn alloy and commercially pure titanium (CP Ti).     

Surface performance and physical properties of nanoscale ceramics reinforced laser alloying composite coatings

Si₃N₄–Ni60 is firstly used to improve the wear resistance of a TA7 (Ti–5Al–2.5Sn) titanium alloy surface by mean of a laser alloying (LA) technique. The synthesis of the hard composite coating on a TA7 titanium alloy by LA of Ni60–Si₃N₄ pre-placed powders was investigated by means of scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and high resolution transmission electron microscope (HRTEM). Experimental results indicated that a number of the interdendritic lamellar eutectics, nanoscale ceramics (NC) and the amorphous phases were produced in such LA coating. The production of NC led the free energy to enhance, which increased the density of point defect, leading to the formation of hypersaturated state of point defect, causing lattice distortions. Compared with a TA7 alloy substrate, an improvement of the wear resistance was obtained for such LA composite coating.     

Bioactive glass induced in vitro apatite formation on composite GBR membranes

The aim of this study was to investigate in vitro bioactivity of different thermoplastic biodegradable barrier membranes. Three experimental GBR membranes were fabricated using Poly(epsilon-caprolactone-co-D: ,L-lactide) P(CL/DL-LA) and particulate bioactive glass S53P4 (BAG; granule size 90-315 microm): (A) composite membrane with 60-wt.% of BAG, (B) membrane coated with BAG; and (C) copolymer membrane without BAG. Membranes were immersed in simulated body fluid (SBF), and their surfaces were characterized with SEM, XRD and EDS after 6 and 12 h and after 1, 3, 5, 7, and 14 days. Calcium phosphate (Ca-P) surface formation was observed on both composite membranes (A and B) but not on the copolymer membrane without bioactive glass (C). The Ca-P precipitation appeared to be initiated on the bioactive glass followed by growth of the layer along the polymer surface. In 6-12 h ion dissolution of the bioactive glass led to formation of the silica rich layer on the surface of the exposed glass granules on composite membrane B whereas only small amounts of silica was observed on the polymer surface of the composite membrane A. At 24 h nucleation of Ca-P precipitation was observed, and by 3-5 days membrane surface was covered with a uniform Ca-P layer transforming from amorphous to low crystalline structure. At 7 days composition and structure of the apatite surface resembled the apatite in bone. Once nucleated, the surface topography seemed to have significant effect on the growth of the apatite layer.     

Low cycle fatigue behaviour of Ti-6Al-5Zr-0-5Mo-0-25Si alloy at room temperature

Low cycle fatigue (LCF) behaviour of the near α titanium alloy, Ti-6Al-5Zr-0.5Mo-0.25Si (LT26A), was investigated in the (a + β) as well as β treated conditions at room temperature. LCF tests were carried out under total strain controlled mode in the range of Δε_t/2: from ±0.60% to ±1.40%. The alloy shows cyclic softening in both the conditions. Also it exhibits dual slope Coffin-Manson (C-M) relationship in both the treated conditions.     

Influence of Zn doping on electrical and optical properties of multilayered tin oxide thin films

In this study, the electrical and optical properties of Zn doped tin oxide films prepared using sol-gel spin coating process have been investigated. The SnO² : Zn multi-coating films were deposited at optimum deposition conditions using a hydroalcoholic solution consisting of stannous chloride and zinc chloride. Films with Zn doping levels from 0–10 wt% in solution are developed. The results of electrical measurements indicate that the sheet resistance of the deposited films increases with increasing Zn doping concentration and several superimposed coatings are necessary to reach expected low sheet resistance. Films with three coatings show minimum sheet resistance of 1–479 kΩ/ in the case of undoped SnO₂ and 77 kΩ/ for 5 wt% Zn doped SnO₂ when coated on glass substrate. In the case of single layer SnO₂ film, absorption edge is 3.57 eV and when doped with Zn absorption edge shifts towards lower energies (longer wavelengths). The absorption edge lies in the range of 3.489-3.557 eV depending upon the Zn doping concentration. The direct and indirect transitions and their dependence on dopant concentration and number of coatings are presented.     

An X-ray diffraction study of defect parameters in a Ti-base alloy

Detailed studies based on the well established method of Fourier line shape analysis have been made on the X-ray diffraction profile of hexagonal titanium alloy of nominal composition Ti-6.58% Al-3.16% Mo-1.81% Zr-008% Fe-0.012% N-0.0078% C. While deformation fault probability, α, has been found to be quite high compared to that of pure titanium, the deformation growth fault parameter, β, shows a negative value ruling out the presence of growth fault in this alloy in the deformed state.     

Preparation of Sm-Ru bimetallic alloy films on Ru(0001) surface by vapour-deposition and annealing

Sm-Ru intermetallic surface alloy films were prepared by vacuum deposition and annealing of rare earth Sm on single crystal Ru(0001) surface. The Ru 3 d and Sm 3 d core level spectra clearly show the formation of surface alloy layers. XPS measurements on surface alloy film revealed an induced peak in the Ru 3 d region at lower binding energy by 1 eV compared to the bulk Ru (elemental) suggesting an electronic effect of alloying and Sm-Ru bond formation. The Sm 3 d _5/2 photoemission peak of Sm film consists of strong features characteristic of Sm(II) with electron configuration 4 f ⁶ (5 d 6 s ) ² and Sm(III) with electron configuration 4 f ⁵ (5 d 6 s ) ³ .It is observed that the Sm(II) feature decreases in intensity upon alloy formation with surface Ru atoms. Oxidation of these films with carbon monoxide indicates alloy breakdown due to the oxidation of Sm atoms selectively. Alloy oxidation also shows a clear shift of Sm 3 d _5/2 feature.     

Development of oxidation resistant coatings for titanium alloys

Abstract

This work addresses the development of a coating to protect the titanium alloy designated IMI834 from oxidation and alpha case formation. This is to enable the safe use of the alloy at relatively high operating temperatures and thereby significantly improve the efficiency of aeroengines. Two different types of surface modification techniques have been employed to coat the titanium alloy: electrodeposition and pack aluminising. Cyclic isothermal oxidation studies revealed that platinum aluminide coating obtained by electrodeposition followed by pack aluminising exhibits good oxidation resistance compared with that exhibited by a plain aluminide coating. Based on results obtained by different techniques, it is suggested that platinum aluminide is a prospective coating material for preventing alpha case formation and protecting against oxidation in components fabricated from titanium alloy IMI834.     

Surface modification tailors the characteristics of biomimetic coatings nucleated on starch-based polymers

This work describes the influence of surface pretreatments over the nucleation and growth of an apatite layer, formed by a biomimetic process, on which a bioactive glass is used as a precursor of the calcium-phosphate (Ca-P) formation on the materials surface. SEVA-C, a corn starch-based biodegradable blend, was used as substrate. The surfaces were pretreated during various periods by: (i) physical methods, namely ultraviolet radiation (u.v.), and over exposure to ethylene oxide sterilization (EtO); and (ii) chemical methods, namely potassium hydroxide (KOH) and acetic anhydride (CH₃CO)₂ etchings. The surface modifications, performed before the production of the biomimetic coatings, resulted in a faster formation of Ca-P nuclei during the first stages of SBF immersion, particularly in the case of the KOH etching. In this case, it was possible to observe a decrease in the average surface roughness, as measured by laser profilometry, and an increase of the hydrophilicity of the material, which was evident from a clear increment in the water-uptake ability and quantified by contact angle measurements. With this treatment it was possible not only to reduce the induction period for the formation of a well defined and dense apatite-like layer, as observed by scanning electron microscopy (SEM), but also to improve the adhesion of the Ca-P layer to the substrate, as confirmed by the adhesion strength tests. For all the studied pre-treatments, the composition of the films, analyzed by energy dispersive spectroscopy (EDS) and identified by thin-film X-ray diffraction (TF-XRD), seems to be very similar to that of human bone apatites.     

Formation of a novel nanocrystalline coating on AZ31 magnesium alloy by bias sputtering

A novel protective coating was deposited on AZ31 magnesium alloy by bias sputtering with a Ti/Al composite target in this study. It was determined by the analysis of EDS and XRD that the coating was mainly composed of Ti₃Al phase. The calculation, based on the Scherrer formula, further revealed the formation of nanocrystalline structure in the coating. SEM and AFM observations showed that the coating was compact and no obvious columnar structure occurred. In corrosion tests, it was found that the coating was more cathodic than the AZ31 substrate and had a good corrosion resistance in a 3.5 wt.% NaCl solution. Accordingly, the AZ31 substrate was protected by this obtained coating.     

Structure and morphology of TiB2 duplex coatings deposited over X40 CrMoV 5-1-1 steel by DC magnetron sputtering

The deposition of titanium diboride (TiB₂) films over tool steel substrates (AISI H13 premium/EN X40 CrMoV 5-1-1) is being investigated due to its excellent corrosion resistance and chemical stability against liquid aluminium. The use of nitrided steels as substrates for TiB₂ deposition may contribute to increase its adhesion and the overall steel resistance in applications such as forging, extrusion and die casting of aluminium. Duplex coatings were obtained by the PVD deposition of TiB₂ films over heat treated and nitrided steel using non-reactive DC magnetron sputtering from a TiB₂ target, varying the substrate bias voltage. Well structured and crystalline TiB₂ films were obtained for the selected deposition conditions, the best crystalline coatings being obtained for the positively biased substrates. Selected films produced over die-casting pins at a bias voltage of +50 V were tested for resistance to liquid aluminium soldering by immersion tests, and compared with the nitrided steel. The duplex TiB₂ coating has a much larger chemical resistance to attack by molten aluminium alloy than the just nitrided steel. Where there is soldering, steel is rapidly attacked and a complex Al-Fe-Si intermetallic forms.     

Multifunctional porous titanium oxide coating with apatite forming ability and photocatalytic activity on a titanium substrate formed by plasma electrolytic oxidation

Plasma electrolytic oxidation (PEO) was used to make a multifunctional porous titanium oxide (TiO₂) coating on a titanium substrate. The key finding of this study is that a highly crystalline TiO₂ coating can be made by performing the PEO in an ammonium acetate (CH₃COONH₄) solution; the PEO coating was formed by alternating between rapid heating by spark discharges and quenching in the solution. The high crystallinity of the TiO₂ led to the surface having multiple functions, including apatite forming ability and photocatalytic activity. Hydroxyapatite formed on the PEO coating when it was soaked in simulated body fluid. The good apatite forming ability can be attributed to the high density of hydroxyl groups on the anatase and rutile phases in the coating. The degradation of methylene blue under ultraviolet radiation indicated that the coating had high photocatalytic activity.     

Nucleation and growth of a multicomponent metallic glass

The metallic glass samples of Fe ₆₇Co₁₈B₁₄Si₁ (2605CO), prepared by the melt spinning technique were procured from the Allied Corporation. The kinetics of crystallization of this multicomponent glassy alloy is studied using differential scanning calorimetry (DSC). The crystallization data have been examined in terms of modified Kissinger and Matusita equations for the nonisothermal crystallization. The results show enhanced bulk nucleation in general. At high heating rates added to it is surface induced abnormal grain growth resulting in fractal dimensionality. 5th IUMRS ICA98, October 1998, Bangalore.     

Microstructures and bond strengths of the calcium phosphate coatings formed on titanium from different simulated body fluids

Calcium phosphate (Ca-P) coatings were deposited on Ti substrates by a biomimetic method from m-SBF and 10× SBF, respectively. Comparative study of microstructures and bond strengths of the Ca-P coatings deposited from those different SBFs was carried out. Effect of the surface roughness of the substrates on the bond strength of the Ca-P coatings was also studied. Scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transformed infrared spectroscopy (FTIR), inductive coupled plasma spectrometry (ICP) and thermogravimetry (TG) were used to characterize the Ca-P coatings. The bond strengths between the coatings and Ti substrates were measured using an adhesive strength test. Results indicated that the ionic concentrations of the SBFs and the surface roughness of the substrate had a significant influence on the formation, morphology and bond strength of the Ca-P precipitates. The induction period of time to deposit a complete Ca-P layer from the m-SBF is much longer, but the Ca-P coating is denser and has higher bond strength than that formed from the 10× SBF. The Ti with a surface roughness of R_a 0.64 µm and R_z 2.81 µm favoures the formation of a compact Ca-P coating from the m-SBF with the highest bond strength of approximately 15.5 MPa.     

Effects of nano-Fe2O3 powder on thermal emission property of microarc oxidation coating on titanium alloy

Abstract

A ceramic coating was formed on the titanium alloy by microarc oxidation in an electrolyte containing nano-Fe₂O₃, emulsifier OP-10 and sodium phosphate. The composition, surface and cross-sectional morphology and the element compositions of the coatings were characterised by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis system. The spectral emissivity of the coatings was measured by a Fourier transform spectrometer apparatus. The bonding strength between the coating and the titanium alloy was studied by tensile strength test. The thermal shock resistance of the coatings was also evaluated. The results showed that nano-Fe₂O₃ was incorporated into the coating, and the coating had high emission at the wavelength range of 3–20 μm. The bonding strength was 33·2 MPa, and after being subjected to severe thermal shocking for 50 cycles, little peeling-off of the coating occurred.     

镍基喷焊涂层与钛合金基体界面特征的研究

考察了三种工艺制备的镍基喷焊涂层与钛合金基体结合界面的组织形貌、涂层横切面上合金元素的扩散和显微硬度的变化,分析了它们的界面特征及影响因素.结果表明:镍基喷焊涂层与基体钛合金的结合是基于合金元素扩散的冶金结合,合金元素的扩散对涂层与基体能否形成冶金结合具有决定性的影响,钛合金表面的活化处理、涂层合金重熔时液态停留时间以及喷焊后进行时效处理是影响合金元素扩散的主要因素.